1. Field of the Invention
This invention relates to image forming apparatus.
2. Description of the Related Art
In an image forming apparatus, when printing on an envelope, if an envelop is transported through a fixing part under the same condition for plain paper, then image quality may decline due to a crease of the envelope, due to that toner comes off the envelope, etc.
A method is proposed to solve the aforementioned problem. In the method, according to the type of a sheet, pressure switching mechanism switches between a normal mode and an envelope mode with changing pushing force per unit area (i.e. pressure) to a heating roller demonstrated by first and second pressure rollers in order to prevent creasing the sheet (See Japanese Laid-Open Patent Application 2004-279702).